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Erza
a) \(\frac{3}{5}-\frac{1}{3}-\frac{1}{6}=\frac{18}{30}-\frac{10}{30}-\frac{5}{30}=\frac{18-10-5}{30}=\frac{1}{10}\)
b) \(\frac{4}{7}\times\frac{5}{8}\times\frac{7}{12}=\frac{4\times5\times7}{7\times8\times12}=\frac{140}{672}=\frac{5}{24}\)
c) \(\frac{25}{28}\div\frac{15}{14}\times\frac{6}{7}=\frac{25}{28}\times\frac{14}{15}\times\frac{6}{7}=\frac{25\times14\times6}{28\times15\times7}=\frac{2100}{2940}=\frac{5}{7}\)
Thấy đúg thì tk nha các bn !!
a,3/5 - 1/3 - 1/6
= 4/9 - 1/6
= 5/9
b,4/7x5/8x7/12
= 5/14 x 7/12
= 5/24
c,25/18 :15/14 x 6/7
= 25/28 x 14/15 x 6/7
= 5/6 x 6/7
= 5/7
\(=\frac{3}{4}\left(\frac{1}{5.9}+\frac{1}{9.13}+...+\frac{1}{41.45}\right)\)
\(=\frac{3}{4}\left(\frac{1}{5}-\frac{1}{9}+\frac{1}{9}-\frac{1}{13}+...+\frac{1}{41}-\frac{1}{45}\right)\)
\(=\frac{3}{4}\left(\frac{1}{5}-\frac{1}{45}\right)\)
\(=\frac{3}{4}\times\frac{8}{45}\)
\(=\frac{2}{15}\)
a)\(\frac{77}{24}\)=\(3\frac{5}{24}\)
b)=10
c)\(\frac{24}{35}\)
a,
\(3\frac{28}{32}=3+\frac{28}{32}=3+\frac{7}{8}=3+0,875=3,875\)
\(7\frac{15}{75}=7+\frac{15}{75}=7+\frac{1}{5}=7+0,2=7,2\)
b,
\(\frac{37}{8}=\frac{8+8+8+8+5}{8}=\frac{8\times4+5}{8}=\frac{8\times4}{8}+\frac{5}{8}=4+\frac{5}{8}=4\frac{5}{8}\)
\(\frac{149}{25}=\frac{100+25+24}{25}=\frac{100}{25}+\frac{25}{25}+\frac{24}{25}=4+1+\frac{24}{25}=5+\frac{24}{25}=5\frac{24}{25}\)
\(\frac{257}{41}=\frac{246+11}{41}=\frac{246}{41}+\frac{11}{41}=6+\frac{11}{41}=6\frac{11}{41}\)
Thấy 1/41+1/42 +......+ 1/60 < 1/40 .20
1/41 +1/42 + .....+1/60<1/2
mà 1/61 +1/62+......+1/80 < 1/60 .20 =1/3
suy ra 1/41+1/42+ .......+1/80 <1/2 +1/3=7/12(đpcm)
Lại có 1/41 +1/42 +.....+1/80 <1/40 .40 =1(đpcm)
ket qua la 30